OCEAN BEACH  Border Patrol agents and San Diego lifeguards are investigating a suspicious boat found on the shore of Ocean Beach Monday morning.

An empty 18-foot bayliner was found about 6 a.m. on Dog Beach just west of Lifeguard Tower 4, said Border Patrol spokesman Michael Jimenez. Border Patrol agents also found two life vests, two empty gasoline cans and four sets of footprints near the boat.

A drug-sniffing dog searched the boat and found one marijuana joint, Jimenez said.

Evidence found in the boat — life vests, empty gasoline cans and footprints — suggests this was a human smuggling operation, Jimenez said.